Position control device

ABSTRACT

A position control device includes a subtracter for subtracting a q-axis current detection value iq from a q-axis current command value iq* to output a q-axis current error Δiq, an adder for adding a q-axis current compensation amount iqc* for compensating for response timing of q-axis current to the q-axis current error Δiq, a q-axis current controller for amplifying an output of the adder by I-P control to calculate a q-axis voltage error Δvq and calculating a q-axis voltage command value vq* on the basis of the q-axis voltage error Δvq, and a second adder for adding a q-axis voltage feedforward amount vqf corresponding to a time derivative value s·iq of the q-axis current to the q-axis voltage command value vq* to calculate a final q-axis voltage command value.

CROSS REFERENCE TO RELATED APPLICATION

The present invention claims priority under 35 U.S.C. § 119 to JapanesePatent Application No. 2018-119061 filed on Jun. 22, 2018, the entirecontent of which is incorporated herein by reference.

TECHNICAL FIELD

The present specification discloses a position control device thatcontrols current for an electric motor (for example, a synchronous motoror an induction motor) and thereby controls a speed or rotation angle(position) of a feed axis or main axis and adopts a PWM invertor as apower converter.

BACKGROUND

A position control device that controls the speed or rotation angle(position) of the feed axis or main axis of a numerical control machinetool often controls a three-phase synchronous motor or induction motor(hereinafter also referred to as a motor) to drive a load such as atable or workpiece connected to the motor. In this configuration, a PWMinverter is usually adopted as the power converter.

Conventionally, motor control requires use of a two-phase rotationalcoordinate system (generally, a magnetic pole direction is referred toas a d-axis and its electrically orthogonal direction as a q-axis) andcalculation of two-phase voltage command values (vd*, vq*) forcontrolling motor current, as well as application of three-phaseconversion and determination of three-phase control voltage commandvalues (vu*, vv*, vw*). Furthermore, the three-phase control voltagecommand values are power-amplified by the PWM inverter to serve as phasevoltages (vu, vv, vw) for driving the motor.

However, conventional position control devices have a problem in that avoltage output becomes discontinuous when a current direction reversesdue to an impact of a dead time that occurs at the time of switching ofa power conversion element such as a transistor adopted in the PWMinverter, and a DIF ripple of a current direction reversal number occursin position deviation DIF, disturbing a work machining surface, wherebymachined surface quality decreases.

For the problem of decrease in the machined surface quality caused bythe DIF ripple due to the dead time, the impact has been conventionallyreduced by dead time compensation as described above. However, it is noteasy to accurately detect the current direction and precisely switch adead time compensation value, and there has been a limit to the DIFripple reduction by the dead time compensation.

The present specification discloses a position control device thatreduces the DIF ripple due to the dead time by improving voltagedisturbance suppression performance and that achieves improvement ofcommand following performance and optimization of command responsetiming.

SUMMARY

A position control device disclosed herein includes an error amplifierthat amplifies a q-axis current error by I-P (Integration-Proportion)control, and adds a q-axis voltage feedforward amount corresponding to aq-axis current command time derivative value to a q-axis voltage commandvalue, and adds a q-axis current compensation amount for optimizingresponse timing of q-axis current to a q-axis current error.

By configuring a q-axis current control loop by the I-P(Integration-Proportion) control, it is possible to improve voltagedisturbance suppression performance and reduce a DIF ripple due to thedead time. In addition, by the q-axis voltage feedforward correspondingto a jerk command value, it is possible to compensate for a q-axisvoltage error and improve position command value following performance.Furthermore, since the q-axis current compensation amount allows foradjusting q-axis current response timing, DIF occurrence duringacceleration/deceleration operation can be suppressed, and a positionalsynchronous relationship with other control axes operated by PI controlcan be maintained.

BRIEF DESCRIPTION OF DRAWINGS

Embodiment(s) of the present disclosure will be described based on thefollowing figures, wherein:

FIG. 1 is a block diagram illustrating an exemplary configuration of aposition control device;

FIG. 2 is a graph showing an example of a speed loop frequencycharacteristic (ωm/ωm*) in the position control device of FIG. 1;

FIG. 3 is a graph showing an example of a position loop frequencycharacteristic (iq/vdis) in the position control device of FIG. 1;

FIG. 4 is a graph showing an example of a DIF ripple due to a dead timein the position control device of FIG. 1;

FIG. 5 is a graph showing an example of a following error duringacceleration/deceleration in the position control device of FIG. 1;

FIG. 6 is a graph showing an example of a following error duringacceleration/deceleration when a q-axis current compensation amount isadjusted;

FIG. 7 is a block diagram illustrating an exemplary configuration of aposition control device of a comparative example;

FIG. 8 is a graph showing an example of a speed loop frequencycharacteristic (ωm/ωm*) in the position control device of thecomparative example;

FIG. 9 is a graph showing an example of a position loop frequencycharacteristic (iq/vdis) in the position control device of thecomparative example;

FIG. 10 is a graph showing an example of a DIF ripple due to a dead timein the position control device of the comparative example;

FIG. 11 is a graph showing an example of a following error duringacceleration/deceleration in the position control device of thecomparative example;

FIG. 12 is a circuit diagram illustrating a voltage output unit for onephase of a PWM inverter;

FIG. 13 is a time chart illustrating a control voltage command value andan output phase voltage for one phase of the PWM inverter;

FIG. 14 is a diagram illustrating an input-output relationship (controlvoltage command value-output phase voltage) for one phase of the PWMinverter.

EMBODIMENTS

First, a DIF ripple will be explained with reference to a comparisonexample. FIG. 12 is a circuit diagram illustrating a voltage output unitfor one phase of a PWM inverter. By performing high-speed switchingcontrol of on/off of a transistor Tr1 and a transistor Tr2, a phasevoltage V output from a circuit of DC voltage Vdc can be changed between0 and Vdc in average. A control voltage command value vo is to commandon/off of the two transistors, V=Vdc while the TR1 is on, and V=0 whilethe TR2 is on. A diode D1 and a diode D2 are for reflux.

FIG. 13 shows an output phase voltage V when the transistor Tr1 and thetransistor Tr2 are switched by a certain control voltage command valuevo. The upper side of FIG. 13 is an example of the control voltagecommand value vo. A dead time Td is a pause time for preventing bothtransistors from turning on simultaneously and causing short circuitbreakdown.

The lower side of FIG. 13 is an output phase voltage V of the PWMinverter at this time. During current outflow OUT, the transistor Tr1 isoff and current flows through the diode D2, and the output voltagebecomes 0, and during current inflow IN, the transistor Tr2 is off andcurrent flows through the diode D1, and the output voltage becomes Vdc.That is, even if the same control voltage command value vo is applied tothe transistors, a difference due to current directions occurs in anoutput average phase voltage V.

FIG. 14 is a diagram illustrating an input-output relationship for onephase of the PWM inverter with the control voltage command value vo onthe horizontal axis and the output phase voltage V on the vertical axis.However, the control voltage command value vo and output phase voltage Vare both expressed as an average voltage corresponding to an on/offduty. A dotted line indicates an input-output relationship during thecurrent outflow OUT, and an alternate long and short dashed lineindicates an input-output relationship during the current inflow IN. Asolid line represents an ideal linear characteristic.

Since the output phase voltage V changes as indicated by an arrow 300when the current direction changes from the current inflow IN to thecurrent outflow OUT, and changes as indicated by an arrow 301 when thecurrent direction changes from the current outflow OUT to the currentinflow IN, the output phase voltage V becomes discontinuous, as a resulta current response delays, and positional deviation DIF occurs as theposition control device.

Therefore, dead time compensation processing is conventionally performedso that the output phase voltage V is on the solid line showing theideal linear characteristic by previously adding, to the control voltagecommand value vo, a dead time compensation value −vod during the currentinflow IN and a dead time compensation value +vod during the currentoutflow OUT and setting a resulting value as an input voltage to the PWMinverter.

FIG. 7 is a block diagram illustrating an exemplary configuration of aposition control device 200 of a comparative example. A position commandvalue X is output from a higher device (not shown) to the positioncontrol device 200 of the example. A rotation angle θm of a motor 100output from a position detector 101 is a position detection value thatindicates the position of a load 102 connected with and driven by themotor, and is subtracted from the position command value X by asubtracter 50 whose output is the position deviation DIF.

The position deviation DIF is amplified by position loop gain Kp timesby a position deviation amplifier 52. In the example, a feedforwardconfiguration is adopted in order to accelerate a command response.Therefore, the position command value X is differentiated by time by adifferentiator 51 and results in a speed feedforward amount ωf. Thespeed feedforward amount of is amplified by total inertia moment J timesincluding the load after being differentiated by time by a differentialamplifier 56, and results in a torque feedforward amount τf necessaryfor acceleration/deceleration operation corresponding to acceleration ofthe position command value. Note that “s” of the differentiator 51denotes a differential operator of Laplace transform.

An adder 53 adds the output of the position deviation amplifier 52 andthe speed feedforward amount of to output a speed command value ωm*. Onthe other hand, a differentiator 54 differentiates a position detectionvalue θm by time to output a speed detection value ωm. A subtracter 55subtracts the speed detection value ωm from the speed command value ωm*,and speed deviation which is an output of the subtracter 55 is amplifiedby PI (Proportional Integration) by a speed controller 57. An output ofthe speed controller 57 and the acceleration/deceleration torquefeedforward amount τf are added by an adder 58 to result in a torquecommand value τc* of the motor.

A current vector control calculation unit 59 is a calculation unit thatcalculates and outputs a q-axis current command value iq*, a d-axiscurrent command value id*, and a power supply angular frequency ω. In amagnet type synchronous motor (PMSM) such as a surface magnet type(SPM), an embedded magnet type (IPM), or a reluctance type, the currentvector control calculation unit 59 calculates the q-axis current commandvalue iq* and d-axis current command value id* from an N−τ(speed-torque) characteristic of the motor and the speed detection valueωm with respect to the torque command value τc*.

In an induction motor (IM), the current vector control calculation unit59 calculates the d-axis current command value id* from the N−τ(speed-torque) characteristic of the motor and the speed detection valueωm and calculates the q-axis current command value iq* from the torquecommand value τc* and a d-axis current detection value id. Furthermore,the current vector control calculation unit 59 calculates a slip angularfrequency φs from the d-axis current detection value id and a q-axiscurrent detection value iq, and adds it and a motor pair-pole numbertimes the speed detection value ωm (not shown) to calculate the powersupply angular frequency ω.

Generally, torque is controlled by the q-axis current in a two-phaserotational coordinate system, so the q-axis current is hereafterreferred to as torque current or torque, depending on the situation.Note that the magnet type synchronous motor (PMSM) is controlled in theslip angular frequency ωs=0, so the power supply angular frequency cooutput from the current vector control calculation unit 59 is the motorpair-pole number times the speed detection value ωm. An integrator 60integrates the power supply angular frequency co by time to output apower supply phase angle θ.

U-phase current iu and W-phase current iw of the motor are detected bycurrent detectors 72 and 73. Note that V-phase current iv can becalculated by iv=−(iu+iw). A three phase→d-q converter 65 calculates andoutputs d-axis current id and q-axis current iq from the U-phase currentiu, W-phase current iw, and power supply phase angle θ by coordinateconversion.

A subtracter 61 subtracts the d-axis current id from the d-axis currentcommand value id* to calculate a d-axis current error Δid. A d-axiscurrent controller 62 includes an error amplifier for amplifying thed-axis current error Δid by PI (Proportional Integration) and anon-interfering compensation unit (not shown) for compensating for aninterference component with the q-axis from the q-axis current commandvalue iq* and power supply angular frequency ω. The d-axis currentcontroller 62 adds an error amplifier output and a non-interferingcompensation value to output a d-axis voltage command value vd*.

A subtracter 63 subtracts the q-axis current iq from the q-axis currentcommand value iq* to calculate a q-axis current error Δiq. A q-axiscurrent controller 64 includes an error amplifier for amplifying theq-axis current error Δiq by the PI (Proportional Integration), anon-interfering compensation unit (not shown) for compensating aninterference component with the d-axis from the d-axis current commandvalue id* and power supply angular frequency ω, and an induced voltagecompensation unit (not shown) for compensating for induced voltage ofthe motor. The q-axis current controller 64 adds an error amplifieroutput, a non-interfering compensation value, and an induced voltagecompensation value to output a q-axis voltage command value vq*.

A d-q→three phase converter 66 calculates and outputs a U-phase controlvoltage command value vu*, a V-phase control voltage command value vv*,and a W-phase control voltage command value vw* from the d-axis voltagecommand value vd*, the q-axis voltage command value vq*, and the powersupply phase angle θ by coordinate conversion.

A dead time compensation value calculation unit 67 performs d-q→threephase conversion (not shown) to calculate and output each phase currentcommand value of the U phase, the V phase, and the W phase from thed-axis current command value id*, the q-axis current command value iq*,and the power supply phase angle θ by coordinate conversion, andcalculates the above-described dead time compensation value (vud, vvd,and vwd) for each phase in order to compensate for phase voltagebecoming discontinuous during direction reverse of the current commandvalue.

An adder 68 adds the dead time compensation value vud to the U-phasecontrol voltage command value vu* and outputs a U-phase control voltagecommand value vuo after the dead time compensation. Also, an adder 69and an adder 70 add the dead time compensation values (vvd, vwd) to thephase control voltage command values (vv*, vw*) and output a V-phasecontrol voltage command value vvo and a W-phase control voltage commandvalue vwo after the dead time compensation, respectively.

As described above, a PWM inverter 71 inputs thereinto the phase controlvoltage command values (vuo, vvo, vwo) after the dead time compensation,power amplifies them, and outputs phase voltages (vu, vv, vw) fordriving the motor. The output phase voltages are applied to therespective phases of the motor to generate respective phase currents.

FIG. 8 shows a speed loop frequency characteristic from the speedcommand value ωm* to the speed detection value ωm by suitably adjustingproportional gain and integral gain in a PI control system of the d-axiscurrent controller 62, the q-axis current controller 64, and the speedcontroller 57 of the position control device 200 shown in FIG. 7. Inthis case, a speed control band (−3 dB down of gain) is about 200 Hz.(Note that this characteristic is evaluated assuming that the speedfeedforward amount of, the torque feedforward amount τf, and a positionloop gain Kp are 0.)

Next, the above-described impact of the dead time causes discontinuityof the output voltage as shown in FIG. 14, so it can be considered asvoltage disturbance to the position control device 200. Therefore, byforming the q-axis voltage command value vq* by adding voltagedisturbance vdis (not shown) to the output of the q-axis currentcontroller 64 of FIG. 7 after suitably setting the position loop gainKp, a response of the q-axis current iq to the voltage disturbance vdisis evaluated.

FIG. 9 shows a position loop frequency characteristic of voltagedisturbance suppression performance (iq/vdis) of the position controldevice 200. Because the q-axis current iq is proportional to the torque,a ripple of the q-axis current iq is proportional to a speed andposition ripple; that is, a DIF ripple. FIG. 10 shows a DIF ripplegenerated when the motor is operated at a constant speed at which thetotal of current direction reversal numbers of the phase currents is 20times per second (20 Hz) after setting an appropriate dead time and deadtime compensation value. In this case, a DIF ripple of 0.4-0.5 μm onboth side amplitude in length conversion (20 mm per rotation of themotor) occurs.

For the problem of decrease in machined surface quality caused by theDIF ripple due to the dead time, the impact has been conventionallyreduced by the dead time compensation as described above. It is noteasy, however, to accurately detect the current direction and preciselyswitch the dead time compensation value, and there has been a limit tothe DIF ripple reduction by the dead time compensation.

A position control device in FIG. 1 is a position control deviceconfigured for reducing the DIF ripple as one advantage. This positioncontrol device will be described below with reference to figures. FIG. 1is a block diagram illustrating an exemplary configuration of theposition control device. Hereinafter, only differences from thecomparative example described above will be described. In addition, FIG.1 illustrates the case of the surface magnet type synchronous motor(SPM).

In the position control device 10 in FIG. 1, an adder 13 adds a q-axiscurrent compensation amount iqc* to a q-axis current error Δiq andinputs a resulting value into a q-axis current controller 11. The q-axiscurrent compensation amount iqc* is a compensation input for adjusting atorque response time, and a calculation output of a later-describedq-axis response compensation amount calculation unit 1. In addition, theq-axis current iq is added to the input of the q-axis current controller11.

An error amplifier of the q-axis current controller 11 uses I-P(Integration-Proportion) control. The I-P control is a known controlmethod and a calculation expression in this case is shown by anexpression (1):

[Expression  1] $\begin{matrix}{{{\frac{G_{cqi}}{s}\left( {{\Delta \; i_{q}} + i_{qc}^{*}} \right)} - {G_{cap} \cdot i_{q}}} = {\Delta \; v_{q}}} & (1)\end{matrix}$

-   -   where, a q-axis voltage error Δvq is an output of the I-P        control, and Gcqi denoting integral gain and Gcqp denoting        proportional gain are gain parameters involved in the I-P        control.

The q-axis current controller 11 includes, other than the erroramplifier for I-P (Integration-Proportion) amplification, anon-interfering compensation unit for compensating for an interferencecomponent with the d-axis from the d-axis current command value id* andpower supply angular frequency co and an induced voltage compensationunit for compensating induced voltage of the motor in the same manner asthe comparative example. That is, the q-axis current controller 11 addsa non-interfering compensation value ωL·id and an induced voltagecompensation value Ke(ω/p) to the q-axis voltage error Δvq which is anoutput of the I-P control and outputs a q-axis voltage command valuevq*. This series of processing is expressed by an expression (2):

[Expression 2]

Vq*=Δvq+ωLid+Ke(ω/p)  (2),

-   -   where p denotes a pair-pole number, L an inductance per phase,        and Ke a torque constant.

An adder 12 adds a q-axis voltage feedforward amount vqf to the q-axisvoltage command value vq* which is an output of the q-axis currentcontroller 11 and forms a q-axis voltage command value which is an inputto a d-q→three phase converter 66. The q-axis voltage feedforward amountvqf is a q-axis voltage compensation value that compensates for theq-axis voltage error Δvq generated corresponding to a jerk command valueto make Δvq=0 and is a calculation output of the later-described q-axisresponse compensation amount calculation unit 1.

FIG. 1 shows the q-axis response compensation amount calculation unit 1that has a block configuration in the case of the surface magnet typesynchronous motor (SPM). A q-axis voltage vq generated by time change ofthe q-axis current iq is shown by expression (3).

[Expression 3]

vq=sL·iq  (3)

A differential amplifier 2 divides the acceleration/deceleration torquefeedforward amount τf by a torque constant Ke for time differentiationand outputs a time derivative value s·iq of the q-axis current. Sincethe acceleration/deceleration torque feedforward amount τf is a torquecommand value proportional to an acceleration command value, this q-axiscurrent is also proportional to the acceleration command value.

Since an amplifier 3 amplifies the output of the differential amplifier2 by the inductance L times, its output becomes the q-axis voltage vqgenerated by time change of the q-axis current iq of the expression (3).Here, the q-axis current and torque and acceleration have a proportionalrelationship, the q-axis current time derivative value s·i isproportional to jerk. That is, the q-axis voltage vq becomes the q-axisvoltage feedforward amount vqf corresponding to a jerk command value.

By performing the above-described compensation processing from awell-known dq coordinate system voltage equation of the SPM, the q-axisvoltage error Δvq of the expression (1) can be made Δvq=0 includingduring acceleration/deceleration operation. On the other hand, in theI-P control, since command following performance in a high-frequencyband is deteriorated as compared with the PI control, a q-axis currentresponse; that is, a torque response tends to be delayed.

The q-axis current compensation amount iqc*, which is an output of theq-axis response compensation amount calculation unit 1, compensates forthe delay of the torque response. When the expression (1) is solved forthe q-axis current error Δiq, an expression (4) is obtained because, inaddition to Δvq=0, s·iq→s·iq* holds under constant jerk.

[Expression  4] $\begin{matrix}{{\Delta \; i_{q}} = {{\frac{G_{cqp}}{G_{cqi}}\left( {s \cdot i_{q}^{*}} \right)} - i_{qc}^{*}}} & (4)\end{matrix}$

Therefore, when the q-axis current compensation amount iqc* is set by anexpression (5), the q-axis current error Δiq is expressed by anexpression (6).

[Expression  5] $\begin{matrix}{i_{qc}^{*} = {G_{iqc}\frac{G_{cqp}}{G_{cqi}}{\left( {s \cdot i_{q}^{*}} \right)\left\lbrack {{Expression}\mspace{14mu} 6} \right\rbrack}}} & (5) \\{{\Delta \; i_{q}} = {\left( {1 - G_{iqc}} \right)\frac{G_{cqp}}{G_{cqi}}\left( {s \cdot i_{q}^{*}} \right)}} & (6)\end{matrix}$

In the expression (6), the q-axis current error Δiq is proportional to aq-axis current command time derivative value s·iq*. That is, under theconstant jerk, a q-axis current response iq is delayed by a constanttime with respect to the q-axis current command value iq*, whichindicates that its q-axis current response delay time can be adjusted byan interpolation constant Giqc.

Because the output of the differential amplifier 2 can be regarded asthe q-axis current command time derivative value s·iq* in FIG. 1,assuming that an amplification factor Cqr of an amplifier 4 isCqr=Gcqp/Gcqi, the q-axis current compensation amount iqc* of theexpression (5) can be derived by amplifying the output by theinterpolation constant Giqc of an amplifier 5.

FIG. 2 corresponds to FIG. 8 of the comparison example, and shows aspeed loop frequency characteristic from the speed command value ωm* tothe speed detection value ωm by suitably adjusting the proportional gainGcqp and integral gain Gcqi in the I-P control of the q-axis currentcontroller 11 of the position control device 10 shown in FIG. 1. Notethat the proportional gain and integral gain of the d-axis currentcontroller 62 and the speed controller 57 are adjusted to the samevalues as in FIG. 8. In this case, a speed control band is about thesame as in FIG. 8.

FIG. 3 corresponds to FIG. 9 of the comparison example, and shows aposition loop frequency characteristic of voltage disturbancesuppression performance (iq/vdis) of the position control device 10shown in FIG. 1. Note that the position loop gain Kp is adjusted to thesame value as in FIG. 9. The DIF ripple in the example is shown in FIG.4.

Here, the dead time, the dead time compensation value, and the motorspeed are set to the same values as in FIG. 10. In FIG. 4, the DIFripple is about 0.05 μm in both-side amplitude and can be suppressed byabout 1/10 as compared with FIG. 10 of the comparative example. This isthe same for the DIF ripple generated due to the dead time.

Next, consideration is given to the position deviation DIF when anS-shaped acceleration/deceleration position command value X is input tothe position control device 10 shown in FIG. 1. FIG. 5 illustrates thecase of setting the interpolation constant Giqc=0. Because the commandfollowing performance of the q-axis current (torque) is deteriorated inthe high-frequency band by the I-P control, the DIF of about 1 μm on oneside occurs during acceleration/deceleration. Note that in FIG. 5 andlater FIG. 11, and FIG. 6, a frequency DIF ripple component generateddue to the dead time is removed.

FIG. 11 shows the position deviation DIF when the same S-shapedacceleration/deceleration position command value X is input into theposition control device 200 in FIG. 7 for comparison. Because of the PIcontrol, the command following performance of the q-axis current(torque) is high and the DIF during acceleration/deceleration can besuppressed to about 0.2 μm on one side.

FIG. 6 shows an example when the response delay time of the q-axiscurrent (torque) is changed by adjusting the interpolation constant Giqcso that the DIF during acceleration/deceleration is small in theposition control device 10 shown in FIG. 1. The DIF duringacceleration/deceleration can be suppressed to about 0.1 μm on one sideand it is seen that a position synchronous relationship can bemaintained even when simultaneously operated with other control axesoperating under the PI control.

The above description is made on an example of the surface magnet typesynchronous motor (SPM), but the technique disclosed herein is alsoapplicable to the embedded magnet type (IPM) and reluctance type andinduction motor (IM), and the same effect can be expected.

In the case of the embedded magnet type (IPM) and reluctance typesynchronous motors, in the q-axis response compensation amountcalculation unit 1, the amplification factor of an expression (7) is setto the differential amplifier 2 in order to calculate the timederivative value s·iq of the q-axis current from theacceleration/deceleration torque feedforward amount if

[Expression  7] $\begin{matrix}{\frac{s \cdot i_{q}}{\tau_{f}} = \frac{s}{p\left\{ {\Phi_{f} + {\left( {L_{d} - L_{q}} \right)i_{d}}} \right\}}} & (7)\end{matrix}$

-   -   where p denotes the motor pair-pole number, Φf an interlinkage        magnetic flux, Ld a d-axis inductance, and lq a q-axis        inductance. Furthermore, an amplification ratio of the amplifier        3 becomes the q-axis inductance lq.

In the case of the induction motor (IM), the amplification factor of anexpression (8) is set to the differential amplifier 2.

[Expression  8] $\begin{matrix}{\frac{s \cdot i_{q}}{\tau_{f}} = \frac{s}{{pMi}_{d}}} & (8)\end{matrix}$

-   -   where M denotes a mutual inductance of one phase. Furthermore,        the amplification factor of the amplifier 3 is a leakage        inductance of one phase Lσ.

1. A position control device using a PWM inverter as a power converterand for arithmetically controlling current for an electric motor by atwo-phase (d- and q-axis) rotational coordinate system, comprising: asubtracter for subtracting a q-axis current detection value from aq-axis current command value to output a q-axis current error; an adderfor adding a q-axis current compensation amount for compensating forresponse timing of q-axis current to the q-axis current error; a q-axiscurrent controller for amplifying an output of the adder by I-P controlto calculate a q-axis voltage error and calculating a q-axis voltagecommand value on the basis of the q-axis voltage error; and a secondadder for adding a q-axis voltage feedforward amount corresponding to atime derivative value of the q-axis current to the q-axis voltagecommand value to calculate a final q-axis voltage command value.
 2. Theposition control device according to claim 1, further comprising aq-axis response compensation amount calculation unit for calculating theq-axis current compensation amount and the q-axis voltage feedforwardamount, wherein the q-axis response compensation amount calculationunit: calculates a time derivative value of the q-axis current from anacceleration/deceleration torque feedforward amount; amplifies the timederivative value of the q-axis current to calculate the q-axis voltagefeedforward amount; and uses a control parameter of the I-P control andan interpolation constant of a q-axis current response delay time tocalculate the q-axis current compensation amount capable of arbitrarilyadjusting the q-axis current error proportional to the time derivativevalue of the q-axis current.